JP2008070274A - Spectrophotometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent saturation of light receiving elements which is apt to saturate by reducing the accumulated charge amount without reducing the signal strength of the light receiving elements compatible with an unnecessarily large wavelength range. <P>SOLUTION: The light emission spectrum of a light source 2 is measured (step S1). A threshold exceeded only by a projecting wavelength band of the spectrum intensity is set based on the light emission spectrum of the light source 2 (step S2). The ratio between the peak value of the wavelength band exceeding the threshold and the set threshold is determined (step S3). The charge accumulation time of the light receiving elements corresponding to the wavelength band not higher than the threshold is set as the longest charge accumulation time among charge accumulation times at which saturation does not occur in any light receiving element (step S4). Based on the ratio between the peak value of the wavelength band exceeding the threshold and the threshold, the charge accumulation time of the light receiving elements corresponding to the wavelength band exceeding the threshold is set (step S5). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical system that splits measurement light, a photodiode array in which a plurality of light receiving elements that receive the dispersed light and perform photoelectric conversion are arranged corresponding to the spectral light, and an optical path of the measurement light The present invention relates to a spectrophotometer including an arranged sample chamber and a signal reading unit for reading out electric charges accumulated in each light receiving element of a photodiode array.

  In a spectrophotometer that uses a photodiode array in which a plurality of light receiving elements (photodiodes) are arranged in the spectral direction, the measurement light is split by the spectral element for each wavelength band and is incident on the light receiving element. In the light receiving element, charges corresponding to the amount of received light are generated and stored by photoelectric conversion. At the time of reading, the amount of incident light on each light receiving element can be measured by sucking and detecting the charge accumulated in each photodiode.

However, photodiodes saturate when a certain amount of charge is accumulated and cannot accumulate more charge, so it is necessary to set the charge accumulation time according to the light receiving element with the strongest spectral intensity so as not to saturate in all light receiving elements. was there. When the charge accumulation time is set in accordance with the light receiving element having the strongest spectral intensity, the amount of charge accumulated in the light receiving element in the wavelength band having the weak spectral intensity is extremely small, and the signal intensity in the wavelength region is weakened.
The readout noise during signal readout is constant regardless of the charge accumulation amount. If the signal intensity is weak, the noise ratio increases, and the measurement error increases. Therefore, in order to reduce the relative ratio of noise and reduce the measurement error, it is preferable to increase the signal intensity by accumulating charges up to the limit of the saturation level of the light receiving element.

Therefore, in order to reduce noise in the entire wavelength range in the absorption spectrum measurement, a control circuit is provided for independently controlling the open / close cycle of the readout switch of each light receiving element constituting the photodiode array, and the charge accumulation time of each light receiving element is provided. Has been proposed to change the charge accumulation time of each light receiving element in accordance with the intensity of the background spectrum (light source spectrum when no sample is placed) (see, for example, Patent Document 1).
In this method, by shortening the charge accumulation time of the light receiving element corresponding to the wavelength band where the spectrum intensity is strong in the emission spectrum of the light source, and increasing the charge accumulation time of the light receiving element corresponding to the wavelength band where the spectrum intensity is weak. The signal intensity in the entire wavelength range can be made uniform. However, since the charge accumulation time must be calculated and set from the spectral intensity of the light source and the target spectral intensity for all the light receiving elements, a control circuit that independently controls the open / close cycle of the readout switch of each light receiving element. There is a problem that the configuration becomes complicated and expensive.

  The measurement wavelength range of the ultraviolet-visible spectrophotometer is 190 nm to 1100 nm. In order to cover this wavelength range, it is common to use a deuterium lamp (hereinafter referred to as D2 lamp) and a tungsten halogen lamp (W lamp) that are simultaneously turned on as a light source. However, the light source spectral characteristics of the D2 lamp and the W lamp are not flat, and the emission line wavelength of the D2 lamp is particularly prominent. When the D2 lamp and the W lamp are turned on at the same time, the 656 nm emission line has the maximum spectral intensity on the visible side, and the light receiving element corresponding to this wavelength band is saturated first. A method of reducing the spectral intensity of the W lamp so that the light receiving element does not saturate is also conceivable, but if the spectral intensity of the W lamp is reduced, the merit of simultaneously lighting together with the D2 lamp is reduced.

Therefore, a method has been proposed in which a light reducing filter is provided on the light receiving surface side of the photodiode array to reduce the incident spectral intensity to the light receiving element corresponding to the wavelength band indicating the protruding spectral intensity (for example, Patent Document 2). reference.).
In this method, for example, in the case of simultaneous lighting of the D2 lamp and the W lamp, the received light amount of the light receiving element corresponding to the emission line wavelength band near 656 nm, which is a peak in the light emission spectrum of the light source, is attenuated by the light reducing filter. By doing so, it is possible to lengthen the time until it is saturated by any one of the light receiving elements of the photodiode array, and it is possible to increase the signal intensity of the light receiving elements in the wavelength band other than the dimmed wavelength band.

JP-A-8-15013 Japanese Utility Model Publication No. 5-79451

  When a light source composed of a D2 lamp and a W lamp is used, the wavelength range of 656 ± 4 nm has the strongest spectral intensity. Therefore, by reducing the accumulated charge amount of the light receiving element corresponding to this wavelength range, The signal intensity of the corresponding light receiving elements can be increased, and the noise ratio of those light receiving elements can be reduced. In the method using the dimming filter, there are restrictions such as processing accuracy, positioning accuracy, adjustment tolerance, and the like. In practice, a wide dimming filter that covers the light receiving element corresponding to the wavelength range of about 656 ± 20 nm is used. It is used. However, in this case, as shown in FIG. 6, there is a problem that the light intensity is unnecessarily reduced in a wide wavelength range, and the spectrum intensity is unnecessarily reduced.

  SUMMARY OF THE INVENTION Accordingly, the present invention aims to reduce the accumulated charge amount of a light-receiving element that is likely to be saturated without lowering the signal intensity of the light-receiving element corresponding to an unnecessarily wide wavelength range so as not to be saturated. is there.

  In the spectrophotometer of the present invention, a light source, an optical system that separates light from the light source, and a plurality of light receiving elements that receive light dispersed by the optical system and perform photoelectric conversion are arranged corresponding to the spectral light. A photo diode array, a sample chamber arranged on the optical path of the measurement light, and a light receiving unit comprising a signal reading unit for reading out electric charges accumulated in each light receiving element of the photo diode array. Can further set a charge accumulation time for each light receiving element of the photodiode array, and further includes a control unit that controls the charge accumulation time of each light receiving element, and the control unit exceeds a preset threshold in the emission spectrum of the light source The charge accumulation time of the light receiving element corresponding to the wavelength band indicating the spectral intensity is relatively shortened.

  Based on the ratio between the peak spectral intensity of the wavelength band showing the spectral intensity exceeding the threshold value and the threshold value in the emission spectrum, the control unit of the light receiving element corresponding to the wavelength band showing the spectral intensity exceeding the threshold value. It is preferable that the charge accumulation time is set to be uniformly shorter than the charge accumulation times of the other light receiving elements.

The light source may generate light whose emission line wavelength band exists as a peak in the emission spectrum within the measurement wavelength range, in which case the threshold is set so that only the emission line wavelength band is exceeded. It is preferable that
An example of such a light source is one in which a deuterium lamp and a tungsten halogen lamp are turned on simultaneously. In this case, the emission line wavelength band is a very small range centered on 656 nm, for example, a wavelength range of ± 4 nm.

  The measurement method of the present invention includes a light source, an optical system that splits light from the light source, and a photodiode array that is arranged corresponding to the spectroscopic light to receive light dispersed by the optical system and perform photoelectric conversion. And a measuring method using a spectrophotometer comprising a light receiving portion comprising a signal reading portion for reading out the electric charge accumulated in each light receiving element of the photodiode array, wherein the light receiving portion receives the light from the photodiode array. Use a device that can set the charge accumulation time for each device, measure the emission spectrum of the light source without a sample, set the threshold based on the emission spectrum, and set the threshold in the emission spectrum. The charge accumulation time of the light receiving element corresponding to the wavelength band showing the spectral intensity exceeding the value is set to be relatively short. That.

  In the measurement method of the present invention, the charge accumulation of the light receiving element corresponding to the wavelength band showing the spectral intensity exceeding the threshold is based on the ratio of the peak spectral intensity of the wavelength band showing the spectral intensity exceeding the threshold and the threshold. It is preferable to set the time uniformly shorter than other charge accumulation times.

  In the spectrophotometer and the measuring method thereof according to the present invention, a light receiving unit that can set the charge accumulation time for each light receiving element of the photodiode array is used, and the spectrum intensity in the emission spectrum of the light source exceeds a preset threshold value. Since the charge storage time of the light receiving element corresponding to the wavelength band indicating the spectral intensity is relatively shortened, the amount of stored charge of the light receiving element corresponding to the wavelength band having a large spectral intensity is relatively reduced, The light receiving element is less likely to be saturated. As a result, the charge accumulation time of the light receiving elements corresponding to other wavelength bands can be made longer than before, so that the signal intensity can be increased and the noise ratio can be reduced.

Based on the ratio between the peak spectral intensity of the wavelength band showing the spectral intensity exceeding the threshold in the emission spectrum and the threshold, the charge accumulation time of the light receiving element corresponding to the wavelength band showing the spectral intensity exceeding the threshold is different. If it is set to be uniformly shorter than the charge accumulation time of the light receiving element, the charge accumulation time in the wavelength band showing the spectral intensity exceeding the threshold value will not be set shorter than necessary, and the light source emits light. The spectrum can be used to the maximum.
Further, by uniformly setting the charge accumulation time of the light receiving element corresponding to the wavelength band showing the spectral intensity exceeding the threshold value, the configuration can be simplified as compared with setting the charge accumulation time for each light receiving element. .

  If a light source that emits light with an emission line wavelength peak in the emission spectrum within the measurement wavelength range is set and the threshold is set to exceed only the emission line wavelength band, the wavelength other than the emission line wavelength band Without lowering the sensitivity of the light receiving element corresponding to the band, the sensitivity can be lowered by setting the charge storage time of only the light receiving element corresponding to the bright line wavelength band of the protruding spectral intensity relatively short.

FIG. 1 is a schematic configuration diagram showing an embodiment in which the spectrophotometer of the present invention is used in a liquid chromatograph.
In this embodiment, the flow cell (sample chamber) 4 in which the eluate from the column of the liquid chromatograph flows is irradiated with light from the light source 2 composed of a D2 lamp and a W lamp, and the absorbance is measured. The light that has passed through the flow cell 4 passes through the slit 6 to form a line beam, and then is split by the spectral element 8 for each wavelength and is incident on the photodiode array 10. In the photodiode array 10, a plurality of light receiving elements made of photodiodes are arranged so as to correspond to the spectral light from the spectral element 8, and each light receiving element receives light for each wavelength band. When each light receiving element of the photodiode array 10 receives light, it performs photoelectric conversion to generate charges, and accumulates a charge amount corresponding to the received light amount. The electric charge accumulated in each light receiving element is read by the signal reading unit 12. The photodiode array 10 and the signal readout unit 12 constitute a light receiving unit. The signal reading operation of the signal reading unit 12 is controlled by the control unit 14.

  The light receiving unit of this embodiment can change the charge accumulation time for each light receiving element of the photodiode array 10, and for example, CMOS linear image sensors S10111 to S10114 series manufactured by Hamamatsu Photonics are used as such a light receiving unit. be able to.

The light receiving unit will be described.
In the light receiving unit of this embodiment, signal reading (scanning) of all the light receiving elements of the photodiode array 10 is sequentially performed by the signal reading unit 12 at a constant cycle. Only the signal read in one scan at a fixed number of times is handled as valid data in the signal reading unit 12, and the data read in the scan in the meantime is discarded. In the following description, a scan for reading a signal handled as valid data is called a valid scan, and a scan for reading a discarded signal is called an invalid scan. The control by the control unit 14 is controlled by the signal reading unit 12 and the handling of signals read by the scan.
One example will be described with reference to FIG. FIG. 4 is a time chart showing signal accumulation / reading operations of the respective light receiving elements of the photodiode array 10.

When the start signal from the control unit 14 becomes a high level, the signal readout unit 12 sequentially outputs a readout signal for controlling on / off of each photodiode to the photodiode array 10. The output of the readout signal by the signal readout unit 12 is controlled by the control unit 14.
When the control signal from the signal reading unit 12 is at a high level (High), each light receiving element accumulates charges as it is, and when the control signal is at a low level (Low), it turns on and discharges the charges. In the example of FIG. 4, the effective scan is performed once every four times, the other is the invalid scan, and the signal read in the invalid scan is discarded as invalid data.

  The light receiving element shown in FIG. 4A is an element from which the signal reading unit 12 first reads a signal after the start signal from the control unit 14 input to the signal reading unit 12 becomes a high level. . In this light receiving element, the read signal remains at a low level (Low) in all the scans, and the charge is discharged and discarded every invalid scan. Therefore, the signal read at the time of valid scan is the amount accumulated from the end of the previous invalid scan until the valid scan is performed, and the charge accumulation time is from the end of the previous invalid scan until the valid scan is performed. Between.

  The light receiving element shown in (B) is an element from which a signal is read after the light receiving element in (A). In this light receiving element, the readout signal from the signal readout unit 12 is at a high level (High) at the invalid scan immediately before the valid scan, and no signal is read out at the invalid scan just before the valid scan. Therefore, after the second invalid scan is completed, the charge is continuously accumulated until the effective scan is performed, and the charge accumulation time of this light receiving element is twice the charge accumulation time of the light receiving element in (A). .

  The light receiving element shown in (C) is an element from which a signal is read after the light receiving element in (B). In this light receiving element, the readout signal from the signal readout unit 12 remains at the low level (Low) at the invalid scan immediately after the previous valid scan, but the readout signal at the subsequent invalid scan is at the high level (High). Thus, in the two invalid scans before the valid scan, the signal is accumulated without being read out. Therefore, this light receiving element charge accumulation time is three times the charge accumulating time of the light receiving element (A).

  The light receiving element shown in (D) is an element for which signal reading is finally performed after the start signal from the control unit 14 input to the signal reading unit 12 becomes high level. In this light receiving element, the readout signal of the signal readout unit 12 is at a high level (High) at all invalid scans, and charges are continuously accumulated after the next valid scan is completed. Therefore, the charge accumulation time of the light receiving element is four times the charge accumulation time of the light receiving element (A).

A method for setting the charge accumulation time of each light receiving element of the photodiode array 10 in the light receiving unit will be described with reference to FIG. FIG. 2 is a flowchart showing a method for setting the charge accumulation time of each light receiving element.
The emission spectrum of the light source 2 is measured (step S1). At this time, the charge accumulation time is set so as not to saturate all the photodiodes. The emission spectrum of the light source 2 is stored in a storage device not shown. A threshold value is set such that only the wavelength band in which the spectral intensity protrudes exceeds the measured emission spectrum of the light source 2 (step S2). A ratio between the peak value of the wavelength band indicating the spectral intensity exceeding the threshold value and the set threshold value is obtained (step S3). The charge accumulation time of the light receiving element corresponding to the wavelength band showing the spectral intensity below the threshold is uniformly set to the longest charge accumulation time that does not saturate any accumulated charge (step) S4). Based on the ratio between the peak value of the spectral intensity exceeding the threshold value and the threshold value, the charge accumulation time of the light receiving element corresponding to the wavelength band indicating the spectral intensity exceeding the threshold value is set (step S5).

  The control unit 14 automatically performs steps S3 to S5 in FIG. 2 and controls the readout signal output from the signal readout unit 12 based on the set charge accumulation time of each light receiving element.

As a specific example of the method for setting the charge accumulation time of each light receiving element of the photodiode array 10, a case where a light source 2 that simultaneously lights a D2 lamp and a W lamp will be described.
FIG. 3 is a diagram showing an emission spectrum of the light source 2, wherein (A) shows the emission spectra of the D2 lamp (solid line) and W lamp (broken line), and (B) shows the D2 lamp and W lamp simultaneously. The emission spectrum when it is lit is shown. In this figure, the vertical axis represents the spectral intensity, and the horizontal axis represents the wavelength.

  When the D2 lamp and the W lamp are turned on simultaneously to cover the wavelength range of 190 nm to 1100 nm, the spectrum of the D2 lamp and the W lamp is synthesized, and the emission line wavelength of the D2 lamp as shown in (B) is 656 nm. The spectral intensity becomes a peak. In this emission spectrum, the emission line wavelength band where the spectrum intensity is prominent is around 656 nm, and the light receiving element corresponding to this wavelength band is saturated first.

Therefore, as indicated by a two-dot chain line in FIG. 3B, a threshold value is set such that only a protruding bright line wavelength band in a minute range centering on a wavelength of 656 nm is exceeded.
When the threshold value is set, the control unit 14 identifies the light receiving element corresponding to the wavelength band near the wavelength of 656 nm indicating the spectral intensity exceeding the threshold value, and the light receiving elements other than the identified light receiving element are identified. Regarding the charge accumulation time, the longest charge accumulation time is set uniformly such that the light receiving elements corresponding to the wavelength band showing the maximum spectral intensity among these light receiving elements are not saturated.

  Next, the control unit 14 determines the charge accumulation time of the light receiving element corresponding to the wavelength band near 656 nm based on the ratio of the threshold value to the spectral intensity of 656 nm and the charge accumulation time of other light receiving elements set in advance. Is set. That is, the ratio of the charge accumulation time of the light receiving element corresponding to the wavelength band near 656 nm and the charge accumulation time of the other light receiving elements is set to a ratio opposite to or close to the ratio of the spectral intensity of 656 nm to the threshold value. Is set. As a result, the signal intensity of the light receiving element corresponding to the wavelength of 656 nm is set to a level that does not saturate, and the emission spectrum of the light source is utilized to the maximum.

  As described above, in the spectrophotometer of this embodiment, the charge accumulation time of the light receiving element corresponding to a very small range centered at 656 nm, for example, a wavelength range of 656 ± 4 nm is relatively shorter than other light receiving elements. Therefore, the charge accumulation time of the light receiving element corresponding to the wavelength band other than the minute range centered at 656 nm can be increased as a whole, and the signal intensity is increased. In addition, since the minimum charge storage time of the light receiving element is set to be relatively short based on the emission spectrum, the light reception in an unnecessarily wide range is performed as in the case of using the light reduction filter as shown in FIG. The emission spectrum of the light source can be used effectively without weakening the signal intensity of the element.

  In this embodiment, the case where the light source 2 is composed of a D2 lamp and a W lamp has been described as a specific example. However, the present invention is not limited to this. For example, a xenon flash lamp or the like is used as the light source. It is also possible to apply it.

It is a block diagram which shows roughly one Example of a spectrophotometer. It is a flowchart figure which shows an example of the setting method of the accumulation time of the light receiving element of the photodiode array of a light-receiving part. It is a figure which shows the emission spectrum of the light source which consists of D2 lamp and W lamp, (A) has each shown the emission spectrum of D2 lamp (solid line) and W lamp (dashed line), (B) is D2 lamp and W The emission spectrum when the lamps are turned on simultaneously is shown. It is a timing chart figure of signal reading by a signal reading part. It is a figure which shows the energy distribution in the photodiode array after accumulation time setting. It is a figure which shows the emission spectrum correct | amended by the conventional method.

Explanation of symbols

2 Light source 4 Flow cell 6 Slit 8 Spectroscopic element 10 Photodiode array 12 Signal reading unit 14 Control unit

Claims (6)

Photodiode array in which a light source, an optical system that splits light from the light source, and a plurality of light-receiving elements that receive light dispersed by the optical system and perform photoelectric conversion are arranged corresponding to the spectral light, measurement In a spectrophotometer comprising: a sample chamber arranged on the optical path of light; and a light receiving portion comprising a signal reading portion for reading out charges accumulated in each light receiving element of the photodiode array.
The light receiving unit can set a charge accumulation time for each light receiving element of the photodiode array,
A control unit for controlling the charge accumulation time of each light receiving element of the photodiode array;
The control unit relatively shortens a charge accumulation time of a light receiving element corresponding to a wavelength band showing a spectral intensity exceeding a preset threshold in an emission spectrum of the light source. The control unit sets the wavelength band indicating the spectral intensity exceeding the threshold based on the ratio of the peak spectral intensity of the wavelength band indicating the spectral intensity exceeding the threshold in the emission spectrum to the threshold. 2. The spectrophotometer according to claim 1, wherein the charge accumulation time of the corresponding light receiving element is set to be uniformly shorter than the charge accumulation time of the other light receiving elements. The light source generates light having an emission line wavelength band as a peak in an emission spectrum within a measurement wavelength range,
The spectrophotometer according to claim 1 or 2, wherein the threshold is set so that only the emission line wavelength band is exceeded. The light source is one in which a deuterium lamp and a tungsten halogen lamp are turned on simultaneously,
The spectrophotometer according to claim 3, wherein the bright line wavelength band is a wavelength band centered at 656 nm. A light source, an optical system that splits light from the light source, a photodiode array that is arranged corresponding to the spectral light to receive light dispersed by the optical system and perform photoelectric conversion, and the photodiode array In a measuring method using a spectrophotometer provided with a light receiving unit consisting of a signal reading unit for reading out the electric charge accumulated in each light receiving element,
Use the one that can set the charge accumulation time for each light receiving element of the photodiode array as the signal reading unit of the light receiving unit,
Measure the emission spectrum of the light source without a sample installed, set a threshold based on the emission spectrum, and correspond to the wavelength band indicating the spectral intensity exceeding the threshold set in the emission spectrum A measurement method characterized in that the charge accumulation time of the light receiving element is set to be relatively short. Based on the ratio between the peak spectral intensity of the wavelength band showing the spectral intensity exceeding the threshold and the threshold, the charge accumulation time of the light receiving element corresponding to the wavelength band showing the spectral intensity exceeding the threshold is calculated. The measurement method according to claim 5, wherein the measurement is set to be uniformly shorter than the charge accumulation time of the other light receiving elements.

Images